Continued Evolution of the WASSTRIP Process

Clean Water Services installed phosphorus recovery on the dewatering return stream at the Durham Advanced Wastewater Treatment Facility (AWWTF) in 2009. In the following years, this change has led to further refinement in how the solids processing and return streams are viewed in the facility. The WASSTRIP process was developed and installed at Durham AWWTF in 2011. Continuous refinement and optimization of the WASSTRIP, nutrient recovery system, and liquid stream biological phosphorus removal has provided further insight in the interaction between all of the processes. Through this development, the process has yielded several benefits including increased nutrient recovery, reduced struvite formation in the digestion process, and successful operation using endogenous respiration to supply VFAs for phosphorus release instead of external carbon sources. Recent testing also indicates that the WASSTRIP process has a significant impact on cations fed to the anaerobic digestion and subsequent dewatering process. The change in monovalent to divalent cation ratio shows correlation with improved dewaterability of the digested sludge.